The invention relates to the field of televisions capable of displaying side by side pictures of substantially equal size from different sources, and in particular, to such televisions having a wide display format ratio screen. Most televisions today have a format display ratio, horizontal width to vertical height, of 4:3. A wide format display ratio corresponds more closely to the display format ratio of movies, for example 16:9. The invention is applicable to both direct view televisions and projection televisions.
Televisions having a format display ratio of 4:3, often referred to as 4.times.3, are limited in the ways that single and multiple video signal sources can be displayed. Television signal transmissions of commercial broadcasters, except for experimental material, are broadcast with a 4.times.3 format display ratio. Many viewers find the 4.times.3 display format less pleasing than the wider format display ratio associated with the movies. Televisions with a wide format display ratio provide not only a more pleasing display, but are capable of displaying wide display format signal sources in a corresponding wide display format. Movies "look" like movies, not cropped or distorted versions thereof. The video source need not be cropped, either when convened from film to video, for example with a telecine device, or by processors in the television.
Televisions with a wide display format ratio are also suited to a wide variety of displays for both conventional and wide display format signals, as well as combinations thereof in multiple picture displays. However, the use of a wide display ratio screen entails numerous problems. Changing the display format ratios of multiple signal sources, developing consistent timing signals from asynchronous but simultaneously displayed sources, switching between multiple sources to generate multiple picture displays, and providing high resolution pictures from compressed data signals are general categories of such problems. Such problems are solved in a wide screen television according to this invention. A wide screen television according to various inventive arrangements is capable of providing high resolution, single and multiple picture displays, from single and multiple sources having similar or different format ratios, and with selectable display format ratios.
Televisions with a wide display format ratio can be implemented in television systems displaying video signals both at basic or standard horizontal scanning rates and multiples thereof, as well as by both interlaced and noninterlaced scanning. Standard NTSC video signals, for example, are displayed by interlacing the successive fields of each video frame, each field being generated by a raster scanning operation at a basic or standard horizontal scanning rate of approximately 15,734 Hz. The basic scanning rate for video signals is variously referred to as f.sub.H, 1f.sub.H, and 1H. The actual frequency of a 1f.sub.H signal will vary according to different video standards. In accordance with efforts to improve the picture quality of television apparatus, systems have been developed for displaying video signals progressively, in a noninterlaced fashion. Progressive scanning requires that each displayed frame must be scanned in the same time period allotted for scanning one of the two fields of the interlaced format. Flicker free AA--BB displays require that each field be scanned twice, consecutively. In each case, the horizontal scanning frequency must be twice that of the standard horizontal frequency. The scanning rate for such progressively scanned or flicker free displays is variously referred to as 2f.sub.H and 2H. A 2f.sub.H scanning frequency according to standards in the United States, for example, is approximately 31,468 Hz.
Television apparatus with conventional format display ratios can be equipped for displaying multiple pictures, for example from two video sources. The video sources may be the tuner in the television, a tuner in a video cassette recorder, a video camera, and others. In a mode often referred to as picture-in-picture (PIP), the tuner in the television provides a picture filling most of the screen, or display area, and an auxiliary video source provides a small inset picture generally within the boundaries of the larger picture. A PIP display mode in a wide screen television apparatus is shown in FIG. 1 (c). In many instances, the inset picture can be positioned in a number of different locations. Another display mode is often referred to as channel scan, wherein a large number of small pictures, each from a different channel source, fill the screen in a freeze frame montage. There is no main picture, at least in terms size. A channel scan display mode in a wide screen television apparatus is shown in FIG. 1(i). In wide screen television apparatus, other display modes are possible. One is referred to as picture-outside-picture (POP). In this mode, several inset auxiliary pictures can share a common boundary with a main picture. A POP display mode in a wide screen television apparatus is shown in FIG. 1(f). Another mode particularly suited for a wide screen television is side by side pictures of substantially the same size, from different video sources, for example two different channels. This mode is illustrated for a wide screen television in FIG. 1(d) for two 4:3 video sources. It will be appreciated that this mode can be considered a special case of the POP mode.
Horizontal scanning is accomplished in the same amount of time in a wide screen television apparatus as in a conventional television apparatus. However, the distance of the horizontal scan is greater in the wide screen television. This will stretch the picture horizontally, creating significant aspect ratio distortion of the images in the displayed picture. Accordingly, problems can be encountered when displaying a video signal having a conventional 4:3 display format ratio on a wide screen television apparatus, for example one having a 16:9 format display ratio. These particular format display ratios would result in a horizontal stretching or expansion by a factor of 4/3. This is a problem for displaying pictures having a 4:3 display format ratio as a main picture and as an auxiliary picture, such as a PIP or POP. This is also a problem for PIP and POP modes even if the main picture originates from a video source having a 16:9 format display ratio which matches the display means of the television apparatus.
Certain digital circuits, sometimes referred to generally as picture-in-picture processors, are available which can implement PIP and channel scan modes in a conventional television apparatus. One such picture-in-picture processor is designated as a CPIP chip and is available from Thomson Consumer Electronics, Inc. The CPIP chip is described more fully in a publication entitled The CTC 140 Picture in Picture (CPIP) Technical Training Manual, available from Thomson Consumer Electronics, Inc., Indianapolis, Ind. Such picture-in-picture processors are not suitable for implementing special display modes, such as PIP, POP and channel scan, in wide screen television apparatus. If an auxiliary picture developed by such a picture-in-picture processor from an auxiliary video source were displayed on a wide screen television apparatus without an external speedup circuit, the auxiliary picture, or pictures, would be geometrically distorted as described above. The auxiliary picture would exhibit a horizontal expansion by a factor of 4/3 due to the wider horizontal scanning of the wider picture tube, whether direct view or projection. If an external speedup circuit were used, the auxiliary picture would appear without aspect ratio distortion, but would not fill the screen or fill the portion of the screen otherwise allotted for the auxiliary display.
A wide screen television can be provided with a signal processor for distorting a video signal, for example an auxiliary video signal, such that upon subsequent display the auxiliary picture will exhibit no image aspect ratio distortion. The distortion can be implemented as an asymmetric compression. The compression factors will depend upon the relative display format ratios of the auxiliary video signal and the wide screen television apparatus. In order to display an auxiliary video signal having a 4:3 display format ratio on a television apparatus having a 16:9 format display ratio, The auxiliary picture will be horizontally compressed by a factor of 4:1 and vertically compressed by a factor of 3:1. In a television apparatus having a different display format ratio, for example 2:1, the horizontal compression factor would be 1.5 times greater than the vertical compression factor. The asymmetric compression produces geometrically distorted pictures which can then be stored in a video memory associated with a picture-in-picture processor. When the asymmetrically compressed auxiliary picture is read out of memory, in accordance with the normal operation the picture-in-picture processor, the resulting auxiliary display exhibits no aspect ratio distortion and is proper size for its intended purpose, whether PIP, POP, channel scan or otherwise. The horizontal expansion realized lay scanning in the wider television tube exactly cancels the extra compression, that is the asymmetric part, done prior to storage in the video memory.